Add the egg mixture to the saucepan.
Turn the heat to low and very quickly cook the mixture — no more than 15 seconds, still whisking constantly.
If your hollandaise sauce doesn't seem thick enough, you can return to the heat and continue cooking it in five second increments — if the heat gets too high you run the risk of the eggs ending up scrambled. Keep whisking the Hollandaise sauce the entire time, until it reaches the consistency you desire.
If the sauce gets too thick, you can thin with a few drops of warm water before serving.